Disposable hypodermic syringes are used in large quantities for administering medication to patients. After use, the syringes must be discarded safely to prevent accidental puncturing of hospital and other personnel with a contaminated cannula.
The conventional hypodermic syringe includes a barrel open at one end to receive a plunger, which, when operated, forces liquid in the barrel out the discharge end through an opening surrounded by a fitting adapted to be connected to a mating fitting on a hub carried by a cannula at a location remote from the scarf, or sharpened end, of the cannula. The cannula is supplied separately in a sterile package and with a protective cap that fits over the scarf end of the cannula and seats snugly on the hub, which carries the cannula fitting.
To use the cannula in the conventional way, it is attached to the barrel of a syringe with the protective cap still in place over the cannula. To load the syringe with medication, the cannula cap is removed and medication is drawn into the syringe barrel. Accidental puncturing during needle recapping at this time is not considered a great risk because the needle is sterile. If accidental puncture occurs, the assembly is discarded.
In prior art practice, once the medication is properly stored in a sterile syringe/cannula assembly, it is administered to the patient by removing the cannula cap and puncturing the patient's skin for either intravenous or intramuscular injection. The needle is then withdrawn from the patient. The used needle, which is still attached to the syringe, is recapped for proper disposal.
Recapping the cannula involves a substantial chance of accidental puncture with the contaminated cannula because the opening of the protective cap is small (about 1/4" in diameter). The probability of accidental puncture is increased because the cap is held in one hand and the syringe in the other, and the hand holding the cap must make the same relative movement toward the scarf which is used to puncture the skin. If the tip of the cannula misses the opening of the cap, puncture of the fingers holding the cap can easily occur. In the past, such punctures were of concern because of hepatitis. With the onset of the acquired immune deficiency syndrome (AIDS), the puncture wound from a contaminated cannula exposes personnel to the risk of contracting AIDS, an even deadlier disease.
Many attempts have been made to solve the problem of accidental puncture by providing a protective sheath which covers the cannula after it is used. Examples of such attempts are shown in U.S. Pat. No. 4,702,738, issued Oct. 27, 1987, to Spencer; U.S. Pat. No. 4,737,144, issued Apr. 12, 1988, to Choksi; and U.S. Pat. No. 4,743,233, issued May 10, 1988, to Schneider. The disadvantage of these prior art sheaths is that they require specially-constructed syringes.
The present invention reduces the risk of accidental puncture with a contaminated cannula by providing a protective device which permits the cannula to be retracted into a sheath as the cannula is withdrawn from the patient, and without requiring relative movement of the hand in the direction which causes the cannula to puncture the skin. With the cannula in the retracted position, personnel are protected from inadvertent puncture by a contaminated cannula. In the preferred form of the invention, the device may be operated with only one hand to retract the cannula in the sheath, thereby minimizing the danger of accidental puncture with the cannula.
The protective sheath of this invention can be used with standard, mass-produced syringes and cannulas of different sizes, and without requiring any special construction of the standard syringe.